i) Field of the Invention
The present invention relates to an optical information storage apparatus for irradiating a predetermined optical information storage medium with light to access the medium, and an optical device for use in the optical information storage apparatus.
ii) Description of Related Art
An optical disk has been heretofore used as an optical information storage medium for recording/reproducing information such as voice, letter, and image in CD, CD-ROM, CD-R, DVD, PD, MO, MD, and the like. In the optical disk, the information is generally recorded in a band-like area surrounded with a concentric or spiral guide groove (track). Moreover, as an optical information storage apparatus for moving a condensing spot along the track of the optical information storage medium to access the information, apparatuses of various modes such as an installed type, car mounted type, and portable type have been developed. Particularly, MD is popular mainly among young people, and the sales of very compact portable apparatuses with sizes close to an optical disk jacket size are on the increase. Furthermore, as an exterior storage apparatus to be attached to a mobile personal computer (PC) or the like, development of the compact optical information storage apparatus has been expected.
In general, the optical information storage apparatus is provided with an optical head for forming a light spot on the optical disk track to access the information. Moreover, in order to develop the aforementioned compact optical information storage apparatus, an optical head has intensely been developed in which a laser diode (LD) as a light source, a beam splitter (BS), a photo detector for monitoring light outputs, an optical component and photo detector for detecting servo or RF signal, and further a preamplifier circuit are unified and integrated, and an optical device unified with the optical component of the optical head has also been intensely developed.
However, in such unified and integrated optical head, it is expected that noise attributed to fluctuation of the condensing spot during movement of the condensing spot along the track, or noise attributed to wobbling for indicating an information address or the like by meander of the track is generated. Therefore, it is desired that a compact optical information storage apparatus be realized by maintaining unity of the optical head and reducing the noise mixed in a reproducion signal.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a compact optical information storage apparatus in which a signal quality is high, reliability of signal reproduction is also high, and high-density recording is possible, and to provide a unified optical device for use in the optical information storage apparatus.
To achieve the object, according to the present invention, there is provided a first optical information storage apparatus comprising: a light source for emitting a light; an objective optical system for concentrating the light emitted from the light source to an optical information storage medium which generates a return light partially including a signal light in accordance with stored information, and for directing the return light from the optical information storage medium to a light source side; and an optical device, positioned between the light source and the objective optical system, for guiding the light emitted from the light source to the objective optical system, and separating the signal light from the return light reflected by the optical information storage medium and returned via the objective optical system.
The optical device comprises: a separation surface for transmitting the light emitted from the light source to the objective optical system, and reflecting the signal light to separate the signal light from the return light; and a reflective surface including a main portion for reflecting the signal light reflected by the separation surface in a predetermined direction, and a mask portion provided with an optical property different from the optical property of the main portion.
In the first optical information storage apparatus of the present invention, the mask portion may absorb the light, the mask portion may transmit the light, the mask portion may reflect the light in a direction different from the direction of reflection by the main portion, or the mask portion may reflect the light in the same direction as the direction of the reflection by the main portion, and generate a phase difference different from the phase difference of the light generated during the reflection by the main portion.
Moreover, in the first optical information storage apparatus of the present invention, the mask portion is preferably provided with the optical property in accordance with a polarization direction.
Furthermore, in the first optical information storage apparatus of the present invention, the mask portion preferably has a band shape which is longitudinal in a direction corresponding to a width direction of the track formed in the optical information storage medium, and more preferably the mask portion is formed in two places apart from each other in the direction corresponding to the width direction of the track formed in the optical information storage medium.
Since the first optical information storage apparatus of the present invention is provided with the aforementioned mask portion, noise is reduced by a first principle described later. Moreover, since the optical device is provided with the reflective surface including the mask portion, it is easy to manufacture or design the aforementioned unified optical device, and the first optical information storage apparatus of the present invention can be realized as a compact apparatus.
When the mask portion absorbs the light, for the first optical information storage apparatus of the present invention, the reflective surface comprises the surface of the optical device, on which the signal light is incident from the inside of the optical device, and the mask portion is preferably constituted by attaching a light absorbing material to the outside of the optical device with respect to a predetermined portion of the reflective surface.
As the mask portion constituted by attaching the light absorbing material in this manner, a light absorbing pigment may be applied, or a tape-like light absorbing material may be bonded.
It is easy to produce the mask portion constituted by attaching the light absorbing material, which can reduce costs of the optical device and optical information storage apparatus.
Moreover, when the mask portion is formed by attaching the light absorbing material, the reflective surface preferably satisfies a total reflection condition.
When the reflective surface satisfies the total reflection condition, a light absorption effect by the light absorbing material is remarkable, and the reflective surface is particularly effective for noise reduction.
Moreover, when the mask portion transmits or reflects the light, in the first optical information storage apparatus of the present invention, the reflective surface comprises the surface of the optical device, on which the signal light is incident from the inside of the optical device, and the mask portion preferably comprises a concave portion or a convex portion disposed on the predetermined portion of the reflective surface.
The mask portion comprising the concave portion or the convex portion can easily be formed by glass molding, which can reduce the costs of the optical device and optical information storage apparatus.
Furthermore, when the mask portion generates a phase difference different from the phase difference of the light generated during reflection in the main portion, in the first optical information storage apparatus of the present invention, the reflective surface comprises the surface of the optical device, on which the signal light is incident from the inside of the optical device, and the mask portion is preferably constituted by forming a dielectric film on the outside of the optical device with respect to a predetermined portion of the reflective surface.
The mask portion with the dielectric film formed thereon is also easily produced, which can reduce the costs of the optical device and optical information storage apparatus.
To achieve the object, according to the present invention, there is provided a second optical information storage apparatus comprising: a light source for emitting a light; an objective optical system for concentrating the light emitted from the light source to an optical information storage medium which generates a return light partially including a signal light in accordance with stored information, and for directing the return light from the optical information storage medium to a light source side; and an optical device, positioned between the light source and the objective optical system, for guiding the light emitted from the light source to the objective optical system, and separating the signal light from the return light reflected by the optical information storage medium and returned via the objective optical system.
The optical device comprises: a separation surface for transmitting the light emitted from the light source to the objective optical system, and reflecting the signal light to separate the signal light from the return light; a reflective surface for reflecting the signal light reflected by the separation surface in a predetermined direction; and a shielding material for shielding a predetermined portion of a flux of the light reflected by the reflective surface.
In the second optical information storage apparatus of the present invention, the shielding material may absorb the light of the predetermined portion, the shielding material may reflect the light of the predetermined portion, or the shielding material may refract the light of the predetermined portion.
Moreover, in the second optical information storage apparatus of the present invention, the shielding material preferably has a band shape which is longitudinal in a direction corresponding to a transverse direction of the track formed in the optical information storage medium, and more preferably the shielding material is formed in two places apart from each other in the direction corresponding to the transverse direction of the track formed in the optical information storage medium.
In the second optical information storage apparatus of the present invention, since the optical device comprises the shielding material provided with a function similar to the function of the mask portion in the first optical information storage apparatus, the noise is reduced in accordance with the first principle described later even in the second optical information storage apparatus. Moreover, since it is also easy to manufacture and design the optical device including the shielding material as the aforementioned unified optical device, and the second optical information storage apparatus of the present invention can also be realized as the compact apparatus.
To achieve the object, according to the present invention, there is provided a third optical information storage apparatus comprising: a light source for emitting a light; an objective optical system for concentrating the light emitted from the light source to an optical information storage medium which generates a return light partially including a signal light in accordance with stored information, and for directing the return light from the optical information storage medium to a light source side; and an optical device, positioned between the light source and the objective optical system, for guiding the light emitted from the light source to the objective optical system, and separating the signal light from the return light reflected by the optical information storage medium and returned via the objective optical system.
The optical device comprises: a separation surface for transmitting the light emitted from the light source to the objective optical system, and reflecting the signal light to separate the signal light from the return light; and a reflective surface for reflecting the signal light reflected by the separation surface in a predetermined direction, and the separation surface and the reflective surface produce a phase difference within xc2x115xc2x0 in total as a result of reflection by the separation surface and the reflective surface.
In the third optical information storage apparatus of the present invention, the separation surface and the reflective surface produce a phase difference within xc2x110xc2x0 in total as a result of reflection by the separation surface and the reflective surface.
According to the third optical information storage apparatus of the present invention, since the phase difference is produced, the noise is reduced by a second principle described later. Moreover, since it is also easy to manufacture and design the optical device which produces such phase difference as the aforementioned unified optical device, the third optical information storage apparatus of the present invention can also be realized as the compact apparatus.
In the first, second, and third optical information storage apparatus of the present invention, the separation surface is preferably a secondary curved surface for transmitting the light emitted from the light source to a concave surface side from a concave surface side and guiding the light to the objective optical system, and particularly the separation surface is preferably a surface comprising a part of a cylindrical surface for transmitting the light emitted from the light source to the concave surface side from the concave surface side and guiding the light to the objective optical system.
Since the separation surface of the secondary curved surface or the cylindrical surface can inhibit generation of the noise as compared with a flat separation surface, the noise reduction in the optical information storage apparatus of the present invention can further be enhanced.
To achieve the aforementioned object, according to the present invention, there is provided a first optical device comprising: a separation surface for reflecting a light having a predetermined property to separate the light of the predetermined property from a light partially including the light of the predetermined property; and a reflective surface including a main portion for reflecting the light, reflected by the separation surface, in a predetermined direction, and a mask portion having an optical property different from the optical property of the main portion.
Moreover, to achieve the aforementioned object, according to the present invention, there is provided a second optical device comprising: a separation surface for reflecting a light having a predetermined property to separate the light of the predetermined property from a light partially including the light of the predetermined property; a reflective surface for reflecting the light, reflected by the separation surface, in a predetermined direction; and a shielding material for shielding a predetermined portion of a flux of the light reflected by the separation surface.
Furthermore, to achieve the aforementioned object, according to the present invention, there is provided a third optical device comprising: a separation surface for reflecting a light having a predetermined property to separate the light of the predetermined property from a light partially including the light of the predetermined property; and a reflective surface for reflecting the light, reflected by the separation surface, in a predetermined direction, and the separation surface and the reflective surface produce a phase difference within xc2x115xc2x0 in total as a result of reflection by the separation surface and the reflective surface.
Additionally, for the optical device of the present invention, only a basic mode will be described here, this simply avoids redundancy, and the optical device of the present invention includes not only the optical device of the aforementioned basic mode but also various modes of optical devices for respective modes of the aforementioned optical information storage apparatuses.